The present invention is directed generally to determining the presence or absence of an object and, more particularly, to verifying the presence or absence of individual dice in a semiconductor wafer that has been cut to separate the individual dice and from which any number of dice have been removed.
Integrated circuits are solid state devices in which electrical components and electrical connections between the components are incorporated into a solid matrix by the strategic placement of various conducting, semiconducting and insulating materials to form and encapsulate the desired circuit in the composite solid matrix. The development of the integrated circuit has led to the miniaturization of electronics by providing a strong matrix to support and protect fragile miniaturized components and connections and by facilitating the placement of the electrical components in close proximity. The integrated circuit has further served to increase the reliability of electronic devices by the elimination of moving parts and fragile electrical wiring and connections.
Integrated circuits are typically mass produced by forming hundreds of circuits, called dice, on a wafer shaped semiconductor substrate, or "wafer". The circuits are formed by depositing a series of individual layers of predetermined materials on the wafer. The individual layers of the integrated circuit are, in turn, produced by a series of manufacturing steps. The precise characteristics of the layers, such as composition, thickness, surface quality, uniquely determine the electronic properties and the performance of the integrated circuit.
The completed circuits are tested to identify circuits that perform according to a design specification, called "good dice", and those circuits that do not perform within specification, "bad dice" The precise location of the individual dice and whether the dice are good or bad is stored for later use in the form of a wafer map.
Following the completion of the circuits, the wafer is cut to separate the individual dice for further processing. Prior to cutting, an adhesive film is attached to the substrate side of the wafer, opposite the circuit layers, to hold the dice in place following the cutting operation. The individual dice are removed from the cut wafer using a die attach machine or another type of pick and place machine. Typically, the locations of the good dice are identified from the wafer map and the pick and place machine is used to pick the good dice from the wafer and place the dice onto substrates, such as lead frames containing the external electrical connections for the integrated circuit, personal computer boards or other mounting surfaces.
Occasionally, due to errors in the manufacturing process, such as wafer or machine misalignment or mechanical wear, a die will be mispicked from the wafer and a bad die may be attached to the substrate. As a result, a bad die may continue through subsequent processing steps until subsequent testing identifies the bad die, at which time the bad die can be removed from the process stream. The continued processing of the bad dice decreases productivity and yield because of wasted manufacturing time and materials.
In addition, generally only the good dice are removed from the wafer, presumably leaving only bad dice on the wafer. Therefore, if a good die remains in the wafer and is inadvertently discarded as a bad die, productivity and yield will be further decreased.
Currently, following the removal of the dice from the wafer, personnel manually inspect the wafer to verify that the correct dice were removed from the wafer and to determine whether any good dice have been inadvertently missed on the wafer or if any bad dice have been placed into subsequent processing stages. The verification procedure is very time consuming making it difficult to identify and remove bad die from the process stream in a timely manner. As such, the present procedure does not prevent the additional waste of manufacturing time and materials on bad dice. In addition, the verification procedure itself is subject to error due to the tedious nature of the procedure, so the present procedure also may not prevent the inadvertent discarding of good dice.
Thus, the need exists for verification apparatuses and methods which overcomes, among others, the above-discussed problems so as to provide for determination and verification of the presence of bad dice remaining in the process stream and to identify good dice being inadvertently removed from the process stream.